1. Field of the Invention
The present invention relates to a display panel and a method of fabricating a display panel, and more particularly, to a liquid crystal display panel and a method of fabricating a liquid crystal display panel.
2. Discussion of the Related Art
During fabrication of a liquid crystal display (LCD) device, a liquid crystal material layer is formed between first and second substrates bonded together with a certain cell gap therebetween, wherein an electric field applied to the liquid crystal material layer through electrodes of the first and second substrates is adjusted to control light transmitted through the liquid crystal material layer.
The first and second substrates are bonded together by a seal pattern formed along an outline of an effective image display region. In addition, ball spacers are randomly scattered on the first or second substrates, or patterned spacers are formed on the first or second substrates by photolithographic processes to maintain a certain cell gap between the first and second substrates. Then, the liquid crystal material layer is injected between the first and second substrates within the cell gap.
A plurality of gate lines are horizontally arranged at regular intervals and plurality of data lines are vertically arranged at regular intervals on the first substrate, wherein pixels are defined at crossing regions of the gate and data lines and arranged in a matrix configuration. In addition, each pixel has a thin film transistor (TFT) that functions as a switching device and a pixel electrode connected to the TFT. Accordingly, the TFT includes a gate electrode patterned with the gate lines and electrically connected to the gate lines, a source electrode patterned with the data lines and electrically connected to the data lines, and a drain electrode patterned with the data lines and the source electrode to be electrically connected to the pixel electrode.
In addition, the second substrate includes red, green, and blue color filters provided between pixels and separated by a black matrix, wherein a common electrode, which corresponds to the pixel electrode, is provided on the second substrate.
Presently, twisted nematic-type (TN) LCD devices are commonly used because the liquid crystal molecules are provided parallel to the first and second substrates and are spirally twisted with a certain pitch. In addition, a long axis of the liquid crystal molecules is aligned so as to be consecutively changed, wherein viewing characteristics are determined according to the aligning of the longer axis and an alignment of a shorter axis of liquid crystal molecules. However, in the TN-type LCD devices, since light is not completely shielded in an OFF state, contrast ratio is poor. Moreover, since the contrast ratio is varied in accordance with the viewing angle, light transmittance when displaying gray scale images is changed. In addition, along left and right viewing angles, light transmittance is symmetrically distributed along wide viewing angles. However, along upward and downward viewing angles, light transmittance is asymmetrically distributed, wherein an image reversal region is created along the upward and downward directions, thereby narrowing the viewing angle.
Accordingly, in order to prevent the narrowed viewing angle of the TN-type LCD device, various solutions have been attempted including the use of a film-compensated mode for compensating a viewing angle with a compensated film. In addition, a multi-domain mode for varying a main viewing angle direction by each domain by classifying a unit pixel into multi-domain and an in-plane switching (IPS) mode for operating liquid crystal molecules by a horizontal electric field has been tried.
According to an aligning method of the liquid crystal molecules, the LCD device can be divided into vertical aligning and horizontal aligning LCD devices. The vertical aligning method is used for processing a substrate surface in order to align a longer axis of liquid crystal molecules along a direction vertical to the surface of the substrate, and the horizontal aligning method is used for processing a substrate surface in order to align a longer axis of liquid crystal molecules along a direction horizontal to the surface of the substrate. In order to realize the horizontal aligning method, a vertical aligning film is formed on the substrate surface, and liquid crystal molecules having negative-type dielectric anisotropy is used.
In the vertical aligning type LCD device, a longer axis of liquid crystal molecules is aligned along a direction vertical to the vertical aligning film when a voltage is not supplied. Conversely, since the liquid crystal molecules having the negative-type dielectric anisotropy tends to slant toward an electric field when a voltage is supplied, the longer axis of the liquid crystal molecules is moved from along the vertical direction to along the horizontal direction toward the vertical aligning film. Accordingly, light can be transmitted through the LCD device.
In contrast to the TN-type LCD device, the vertical aligning type LCD device is superior in contrast ratio and response time. In addition, when an aligning direction of the liquid crystal molecules is divided into different directions and a compensated film is used, the vertical aligning type LCD device can effectively obtain a wide viewing angle.
In order to fabricate the vertical aligning type LCD device, a technique for aligning the liquid crystal molecules along a desired direction is applied that includes distorting an electric field supplied to a liquid crystal material layer with a side electrode patterned on a first substrate surface and a rib, or a slit formed on the second substrate surface.
The vertical aligning type liquid crystal display panel will be described in detail with reference to accompanying drawings.
FIG. 1 is a cross sectional view of a unit pixel of a vertical aligning type LCD panel according to the related art. In FIG. 1, a first substrate 10 and a second substrate 20 are together so as to have a cell gap formed therebetween, and a liquid crystal material layer 30, which includes liquid crystal molecules 31 that are vertically aligned, is formed in the cell gap between the first and second substrates 10 and 20. In addition, the first substrate 10 is a thin film transistor (TFT) array substrate of the LCD panel, and the second substrate 20 is a color filter (CF) substrate of the LCD panel.
The first substrate 10 includes side electrodes 12 patterned at regular intervals on a surface of a transparent glass substrate 11, a gate insulating film 13 and an active layer 14 sequentially formed on the surface of the transparent glass substrate 11 upon which the side electrodes 12 are formed, data lines 15 patterned at regular intervals on a surface of the active layer 14, gate lines (not shown) patterned at regular intervals on a surface of the gate insulating film 13, a passivation layer 16 formed on another surface of the active layer 14 upon which the data lines 15 are formed, and a pixel electrode 17 patterned on a surface of the passivation layer 16 corresponding to separated regions of the data lines 15.
The second substrate 20 includes a black matrix 22 formed on a first surface portion of a glass substrate 21 corresponding to the data lines 15, a color filter 23 formed on a second surface portion of the glass substrate 21 upon which the black matrix 22 is formed corresponding to the pixel electrode 17, a common electrode 24 formed on the glass substrate 21 upon which the black matrix 22 and the color filter 23 are formed, and a rib 25 formed on a central portion of the common electrode 24 between adjacent portions of the black matrix 22.
An aligning direction of the liquid crystal molecules 31 vertically aligned in the liquid crystal material layer 30 is varied by a vertical electric field supplied by the pixel electrode 17 formed on the first substrate 10 and the common electrode 24 formed on the second substrate 20. However, viewing angle characteristics of the LCD device deteriorate.
Supplying a certain voltage to the common electrode 24 and to the side electrodes 12 formed on the first substrate 10 distorts a vertical electric field applied to the liquid crystal layer 30. Accordingly, the distorted electric field includes multi-domains that are symmetrically partitioned along left, right, upward, and downward viewing angle directions due to the rib 25 formed on the common electrode 24. Thus, a wide viewing angle of the LCD device can be realized.
According to FIG. 1, a method of fabricating a vertical aligning type LCD panel includes patterning the side electrodes 12 at regular intervals on the surface of the transparent glass substrate 11, wherein the side electrodes 12 are patterned together with gate lines (not shown) and the gate electrodes (not shown) formed on the transparent glass substrate 11. In addition, the side electrodes 12 are patterned to be electrically disconnected with the gate lines and the gate electrodes along an outline of a unit pixel. Moreover, the gate insulating film 13 and the active layer 14 are sequentially formed on the surface of the transparent glass substrate 11 upon which the side electrodes 12 are patterned. The gate insulating film 13 and the active layer 14 are sequentially formed to form a TFT included in the unit pixel of the transparent glass substrate 11.
Then, the data lines 15 are formed at regular intervals on the surface of the active layer 14. Although not shown, the source electrode and the drain electrode of the TFT are simultaneously patterned together with the data lines 15. In addition, the data lines 15 are vertically arranged at regular intervals, the gate lines (not shown) are horizontally arranged at regular intervals, and the unit pixel is defined as a rectangular region formed by crossings of the data lines 15 and the gate lines (not shown). The side electrodes 12 are patterned along the outline of the unit pixel to not be overlapping with the gate lines (not shown) and the data lines 15.
The active layer 14 includes a semiconductor layer made of amorphous silicon and an ohmic contact layer made of n+ amorphous silicon doped with phosphorus (P) at a high concentration, which are sequentially deposited and patterned. When the data lines 15 and the source electrode and the drain electrode are patterned, an exposed portion of ohmic contact layer is removed to form a channel of the TFT. Accordingly, only the semiconductor layer remains.
In addition, the passivation layer 16 is formed on the surface of the active layer 14, wherein the passivation layer 16 is formed of a thin film made of an inorganic material, such as SiNx or SiOx. However, in order to improve an aperture ratio of the LCD device, a thick film made of an organic material, such as benzocyclobutene (BCB), spin on glass (SOG), or photo-acryl, having a low dielectric constant may be applied. Then, the passivation layer 16 is selectively etched to form a drain contact hole (not shown) for exposing a part of the drain electrode (not shown).
The pixel electrode 17 is patterned on the surface of the passivation layer 16 to correspond with separated regions of the side electrodes 12. Accordingly, the pixel electrode 17 is electrically connected to the drain electrode (not shown) of the TFT through the drain contact hole (not shown) formed on the passivation layer 16.
Then, the black matrix 22 is coated on the surface of the transparent glass substrate 21 of the second substrate 20 along the outline of the unit pixels of an image display region. Next, the R, G, and B color filter 23 corresponding to the unit pixels of the image display region is formed on the surface of the transparent glass substrate 21 upon which the black matrix 22 is formed. Then, the common electrode 24 is formed on the surface of the glass substrate 21 including the black matrix 22 and the color filter 23. Accordingly, the black matrix 22 is formed on the regions corresponding to the gate lines, the data lines 15 and the TFT that have been formed in the image display region of the first substrate 10. The black matrix 22 prevents transmission of R, G, and B colored light through the color filter 23 of adjacent units pixels, thereby preventing deterioration of image quality of the LCD panel.
Next, as shown in FIG. 1, the rib 25 is formed on the surface of the common electrode 24 to corresponded to the central portion of the pixel electrode 17. Then, the first and second substrates 10 and 20 are bonded together by a seal pattern such that the pixel electrode 17 and the common electrode 24 correspond to each other.
FIG. 2 is cross sectional view of a unit pixel of a vertical aligning type LCD panel according to the related art. In FIG. 2, side electrodes 32 are formed on the transparent glass substrate 11 of the first substrate 10 by simultaneous patterning of the gate electrode (not shown), and the gate lines (not shown) are formed on the passivation layer 16 by simultaneous patterning of the pixel electrode 17. Accordingly, the side electrodes 32 are formed to be uniformly separated from the pixel electrode 17. In addition, instead of the rib 25 (in FIG. 1) being formed on the common electrode 24 of the second substrate 20, a slit 36 may be formed by etching the common electrode 24. For example, side electrodes 32 are patterned on the passivation layer 16 together with the pixel electrode 17 so as to be uniformly separated from the pixel electrode 17, and the slit 36 is formed in the etched region of the common electrode 24.
In FIGS. 1 and 2, the side electrodes 12 and 32 of the vertical aligning type LCD panels are formed along the outline of the unit pixel defined as a rectangular region by the crossed gate lines (not shown) and the data lines 15, and the pixel electrode 17 is patterned at regions between the side electrodes 12 and 32 of the unit pixel. Accordingly, an effective liquid crystal control region of the unit pixel that corresponds to the pixel electrode 17 on the first substrate 10 and the common electrode 24 on the second substrate 20 is reduced due to the side electrodes 12 and 32 that are formed along the outline of the unit pixel, whereby an aperture ratio of the LCD device is reduced. In addition, an alignment direction of the liquid crystal molecules 31 is changed by distorting the vertical electric field supplied between the pixel electrode 17 and the common electrode 24 by the side electrodes 12 and 32. Accordingly, an alignment of the liquid crystal molecules 31 is dispersed by the voltage variation of the data lines 15, whereby light leakage occurs in boundary regions of the data lines 15 and the pixel electrode 17 and image quality is reduced.